Induction of cardioplegia is known in the art as a means for the temporary and elective stopping of cardiac activity by injection of chemicals, selective hypothermia, mechanical stabilization, or electrical stimuli. It is most commonly used in preparation for cardiac surgery.
PCT patent application PCT/IL97/00012, published as WO 97/25098, to Ben-Haim et al., which is incorporated herein by reference, describes methods for modifying the force of contraction of at least a portion of a heart chamber by applying a non-excitatory electrical signal to the heart at a delay after electrical activation of the portion. The signal may be applied in combination with a pacemaker or defibrillator, which also applies an excitatory signal (i.e., pacing or defibrillation pulses) to the heart muscle.
PCT patent application PCT/IL97/00236, which is also incorporated herein by reference, describes a pacemaker that modifies cardiac output. This pacemaker applies both excitatory (pacing) and non-excitatory electrical signals to the heart. By applying non-excitatory signals of suitable strength, appropriately timed with respect to the heart's electrical activation, the contraction of selected segments of the heart muscle can be increased or decreased, thus increasing or decreasing the stroke volume of the heart. The PCT application suggests that pacing electrodes may be placed in two, three or all four chambers of the heart, in accordance with methods of multi-chamber pacing known in the art.
U.S. Pat. No. 5,651,378 to Matheny et al., and an article entitled, "Vagus Nerve Stimulation as a Method to Temporarily Slow or Arrest the Heart," by Matheny and Shaar, Annals of Thoracic Surqery, 63 (6) Supplement (June 1997), pp. S28-29, which are both incorporated herein by reference, describe a method to stimulate the vagus nerve in order to slow or stop a patient's heart during coronary artery bypass grafting surgery. While these methods describe electrically-stimulating the vagus nerve, they are, overall, substantially similar to chemical means of inducing cardioplegia, and are therefore characterized by a generally slow time constant following application and removal of the vagal nerve stimulation.